1. Field of the Invention
This invention relates to a process for making cellular material and more particularly to a process for first sintering a mixture of pulverulent batch and cellulating agent for a preselected period of time, terminating the sintering of the material and thereafter heating the sintered material to a cellulating temperature to form a cellular material.
2. Description of the Prior Art
U.S. Pat. No. 2,736,142 to Baumler et al describes a process for manufacturing cellulated material and eliminating the flaws that are found in the blocks of cellulated material caused by uneven heating and the like. In this process the pulverulent glass batch is positioned in a mold and thereafter a dicing device is inserted into the layer of pulverulent batch to form generally rectangular cubes of the pulverulent batch. Thereafter, the dicing device is removed and the diced pulverulent batch in the mold is subjected to a heating schedule which includes heating the pulverulent batch at a sintering temperature for a sufficient period of time for the pulverulent batch to soften and coalesce. The temperature is then slowly increased to the cellulating temperature where the pulverulent batch reacts with the cellulating agent to cellulate the material. It is stated in U.S. Pat. No. 2,736,142 that the diced arrangement of the pulverulent batch eliminates the imperfections, i.e., folds and uneven densities in the cellular material. In Baumler, however, a conventional heating schedule is utilized and requires the material to remain in the cellulating furnace for a substantial period of time.
U.S. Pat. No. 2,775,524 is directed to a method for producing cellulated articles by coating the carbonaceous cellulating agent on an inert substance having a high surface area and heating the coated article in the presence of air to about 570.degree. F. (300.degree. C.) to form a black char. This black char is mixed with conventional glass cullet and the admixture is cellulated in a conventional manner.
U.S. Pat. No. 3,532,480 is directed to a method of making cellular glass by first agglomerating the discrete powdery mixture of pulverulent glass and cellulating agent into pellets and heating the pellets to an elevated temperature so that the pellets partially cellulate and cohere to each other to form a sheet of coalesced partially expanded pellets. The sheet of coalesced partially expanded pellets in a plastic state is fed into a heating chamber where the sheet of coalesced partially expanded pellets further cellulate to form a sheet of cellular glass.
U.S. Pat. No. 4,075,025 discloses a process of forming a potassium aluminoborosilicate frit by preparing an aqueous slurry of colloidal silica, caustic potash, boric acid and alumina. The slurry is dried and the aggregates are thereafter crushed, calcined and rapidly quenched. The calcined mixture of the above constituents is introduced into a crusher such as a ball mill and the carbonaceous cellulating agent is also introduced into the crusher to form a homogeneous admixture of the calcined mixture and the cellulating agent. The admixture, as a fine pulverulent material is then cellulated in a conventional manner to form cellular borosilicate bodies. In the above process, only the pulverulent constituents are calcined and thereafter the calcined material is admixed with the carbonaceous cellulating agent.